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Old 10-20-2019, 06:40 AM   #1
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Default Mercruiser 496 intermittent alarm and revs drop

I have a 2006 Maxum 2700SE with a 2006 Mercruiser 496 mag, 0W632320 with Bravo 3. Boat lives dry in a floating dock and I fresh water flush most trips.

Boat runs well at all ranges, but I get this intermittent single beep on the alarm, revs drop for an instant and immediately pick back up again and we carry on as normal.

It seems quite random but tends to happen within first 5 minutes after starting (hot or cold) and usually happens with RPM less than about 2000. Donít recall it ever happening at higher revs.

last time I went out I did a bunch of runs to try and figure out what is happening. I did about 7 or 8 starts and it happened every time.
I noticed that when the beep occurred the revs dropped to about 600 - you can feel the boat slow momentarily- but it doesnít sound like it is running rough or misfired- the alarm is a single beep for about a second. Boat then carries on running as normal. This was happening shortly after starting up - within a few minutes.

The revs in the Smartcraft tacho drop and the digital voltage display on the Smartcraft gauge goes down to 0 volts for a few seconds but the display stays live. The analog voltage gauge doesnít move.

I have VesselView mobile and get no faults or warnings.

I started checking all of the connections to see if it could be a ground short but havenít found any loose or damaged connections.

I checked the ignition harness connection at the engine and that seems ok.

Strangely enough - I disconnected all of the Smartcraft gauges and just left the VesselView hooked up and the problem became a lot less frequent - I managed about 10 starts all ok and then the last run it happened after about 20-25 minutes.

Any ideas on what to check next?

How would I do a continuity test on the ignition to engine harness.

Thanks for any ideas.

Andy

























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Old 10-20-2019, 12:03 PM   #2
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Have you checked the fluid levels; engine oil and gear lube?
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Old 10-20-2019, 10:09 PM   #3
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Thanks- Yeah, checked all the fluid levels. All seem fine. Also - just for interest and to see if it was a problem with the lube oil sensor - I pushed the float in the lube oil monitor down to see if it gave the same alarm - and it didnít. The lube oil alarm was multiple beeps and a fault code on the Smartcraft gauge and VesselView mobile.


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Old 10-20-2019, 10:45 PM   #4
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Thanks for reporting you findings on the fluids. Have you googled Mercruiser MPI fault codes?
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Old 10-21-2019, 12:52 AM   #5
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I couldnít see any of the fault codes / alarms that matched my symptoms. I am now working my way through the PCM-555 Diagnostic Manual to see if there are any clues.
They seem to indicate a connection or harness fault.


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Old 06-26-2021, 12:59 PM   #6
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Default Same issue

Hello! I reaaly want to know if ,and how, you sorted this issue out. I have been struggling with the same issue for quite some time on a merc 4.3 MPI with no success.
Will you please enlighten me on your methods?
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Old 07-29-2021, 03:07 PM   #7
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Default Intermittent alarm and rev drop

Have same problem. No one can figure out. Swapped parts from one engine to the other. ICM, computer, fuel lines, complete tune up, wires, plugs, rotor, cap. Even isolating battery. Took small trip. Engine quit leaving dock. Started right back up and traveled slow up river, alarm still sounding and dropping 100 rpm. Went to cruising speed, ran fine, got to dock and traveled slow down river, in and out of gear, nothing. Waited 5 minutes and started to see if problem was over, nope same problem still there. Someone told me fuel pump overheats and need a extra fuel line pump inline to come on with factory pump. Yet, I ran fuel pressure test and no problem. He said Mercruiser knows this. Waiting for mechanic to check. One mechanic took engine analyzer and said it don't show. Hopefully will find out soon. Let me know if you find anything. Mercruiser don't answer phone.
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Old 07-29-2021, 03:26 PM   #8
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Iíve never heard of the fuel pump overheating but have heard about debris in the cool fuel system from paint flakes causing issues. Solution was to replace it.
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Old 07-29-2021, 08:06 PM   #9
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I never heard overheating either. But this guy told me he gave a guy an external fuel pump and problem solved. Said it overheats down under the engine. I didn't believe it either. Because, if hatch is open and only ran 1 minute, hwo could it over heat. I will keep posted if I find out the problem. Funny, no one knows what's wrong, yet I'm seeing others with the same problem
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Old 08-09-2021, 07:01 PM   #10
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My problem gets less and less happening. Had mechanic run more test. Engine was actually shutting down for a second. Shut his computer off the test each time. We changed ignition, still doing it. He left me a wiring harness with a starter. It slowed down a couple time. switched back over to boat harness, same thing. But now it is long in between. Had engine running about a half hour and did one time. Mechanic did clean wiring harness connection, but it stared taking a longer time acting up before. Seems to be curing itself. Just don't know
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Old 08-09-2021, 07:02 PM   #11
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I heard of external pump to. Don't make sense.
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